By: Dr. Gard Otis
Professor Emeritus, University of Guelph, Canada and Research Associate,
Institute of Bee Health, University of Bern, Switzerland gotis@uoguelph.ca
The Yellow-legged Hornet (YLH), frequently referred to as the “Asian hornet” in Europe, is a very serious invasive pest. The first reports of the YLH in the Americas came from Savannah, Georgia, in late Summer of 2023. Despite extensive efforts in both Georgia and South Carolina to trap overwintered queens in Spring and to destroy nests over the next two Summers, this invasive species likely is established now in southeastern USA. This is not good news for U.S. beekeepers.
Vespa velutina var. nigrithorax (Fig. 1), the form of the YLH that inhabits eastern China and northern Vietnam, has a history of invasions. It first was detected outside of its native range in 2003 in South Korea. It has since colonized all of South Korea, is more common there now than any of the seven native hornet species, and has colonized Kyushu Island in southwestern Japan. In Europe, it was first observed in southwestern France in 2004. It has invaded much of western Europe (the progression of the European invasion can be viewed at Rome, 2026) and continues to expand its range in Europe and beyond. During 2025 it was reported for the first time in New Zealand, North Africa (Algeria), Northern Ireland, Denmark, Sardinia and the Azores islands.
The annual life cycle of the YLH is much like that of other social wasps in the USA. Beginning in early Spring, overwintered queens emerge from their wintering sites and feed on floral nectar and tree sap. It is at this time of year that most natural dispersal occurs, with some queens flying 40 miles or more before initiating a primary (“embryo”) nest in a protected site such as the eaves of a building or bush. In most instances, colonies abandon their initial nest during Summer and move to a secondary nest they construct high in a tree where their population continues to grow to hundreds, sometimes more than 1000 worker hornets. In September, brood rearing switches from workers to reproductives, with each colony usually producing a hundred or more virgin queens as well as males. After mating, queens are thought to move only a short distance before entering Winter diapause (a quiescent physiological state) under tree bark, among logs and firewood, under moss and rocks, or in some other protected site. By early Winter the colonies that reared them have usually died.
Two aspects of this life cycle deserve further comments. Unlike honey bees that obtain proteins and fats from pollen, hornet larvae are fed insects and carrion. By late Summer, when hornet colonies are becoming populous and are rearing many larvae, they require large quantities of food. It has been estimated that a single large YLH colony consumes nearly 25 lbs of prey in a year! Honey bee colonies, with their thousands of worker bees in a fixed location, become the focus of much of the hornets’ hunting (Fig. 2). The bees, in response to being attacked by several hornets simultaneously, reduce their foraging due to the risk of predation. The “foraging paralysis” created by ever-present hornets often results in weak Fall colonies with little stored honey, many of which subsequently starve during Winter. As one would expect, these effects on bee colonies are proportionate to the abundance of hornets nearby, so the effects on bee colonies are variable, ranging from extremely high mortality in some regions to inconsequential effects in others. It is too early to predict how seriously the YLH will affect honey bees in the USA, but where they become common they will disrupt beekeeping. In some regions of Europe they cause additional harm by damaging late season fruit crops, particularly wine grapes.
Secondly, during their Winter diapause, hornet queens are immobile for several months. During this time, they can be accidentally transported long distances as stowaways in cargo on ships, which is almost certainly how they reached France, New Zealand, and the USA. Based on European experiences, in addition to the natural spring dispersal of overwintered queens, we can also expect to see “bridgehead” populations popping up far from the main population in southeastern USA as wintering queens get transported by trucks and trains. This is almost certainly how YLHs got to York Co., South Carolina, only 30 miles southwest of Charlotte, NC. Considering the rapid growth of YLH populations in several European countries, I anticipate that the area it inhabits in the Low Country of GA and SC (Fig. 3; Google, 2026) will approximately double this year. Its range should expand further towards the northeast than to the south, as has been observed so far, due to the prevailing southwesterly winds in spring when queens are naturally dispersing. Modelling studies predict that the YLH can survive in much of eastern USA where the climate is relatively moist and the mean annual temperature exceeds 50 degrees F (10 degrees C, e.g. Detroit and Pittsburgh) as well as parts of the Pacific Northwest.
Beekeepers and members of the public can contribute to tracking the invasion of the US by the YLH. Like honey bees, YLHs are not aggressive when foraging and can be approached closely as they feed on sap from tree wounds, flowers, fallen fruits, and carrion. Whenever you visit your apiaries, but especially from mid-August onwards, keep a lookout for large wasps (about one and a half times longer than a honey bee) with yellow legs, hovering in front of hive entrances (Fig. 1). If you suspect you may have observed a Yellow-legged Hornet, write a detailed description of its size, color pattern, and behavior. Even better, take photos of it, alive or dead, at different angles. Then, share your information with your local apiary inspector or state apiarist. Many states now have websites that allow you to submit your sightings online. You may want to share your photos on the citizen-science platform iNaturalist, which is where I learned that the hornet had reached the USA. The Yellow-Legged Ledger (2026) for Georgia and the Hornet Herald (2026) for South Carolina provide many images of the hornets, their nests, and similar species to help with identification, so familiarize yourself with this new pest. If you discover that your bee hives are being heavily attacked, contact agricultural and apiary personnel who may be able to help you locate and destroy the hornet colony. You may want to purchase or make some of the YLH traps that have been developed in Europe and seem to reduce the predation on bees in apiaries.
Interested readers can find additional information about invasive hornets and their effects in Monceau et al. (2014) and Otis et al. (2023).
Acknowledgments
Dr. Lewis Bartlett, University of Georgia, confirmed the March 2026 capture of overwintered queens near Statesboro, GA. Dr. Sandra Rojas shared information on wintering sites of queens. Quentin Rome kindly shared his photo of a hornet dismembering a bee.
References
Hornet Herald (2026). Hornet Herald, Regulatory Services website of Clemson University, SC. https://blogs.clemson.edu/regulatory/2026/02/
Georgia map (2026). Yellow-Legged Hornet Eradication Public Information Dashboard, Georgia Department of Agriculture. https://agr.georgia.gov/yellow-legged-hornet-eradication-map
Google (2026). Google Maps (Map). https://www.google.com/maps
Monceau, K., O. Bonnard, and D. Thiery (2014.) Vespa velutina, a new invasive predator of honeybees in Europe. Journal of Pest Science 87: 1-16. https://link.springer.com/article/10.1007/s10340-013-0537-3
Otis, G.W., B.A. Taylor, and H.R. Mattila (2023) Invasion potential of hornets (Hymenoptera: Vespidae: Vespa spp.). Frontiers in Insect Science 3: #1145158. https://www.frontiersin.org/journals/insect-science/articles/10.3389/finsc.2023.1253176/full
Rome, Q. (2026). Distribution of Vespa velutina in Europe. https://assets.patrinat.fr/files/donnees/carto_frelon/Cartes_Vespa_velutina_2026.zip
South Carolina maps (2026). Hornet Herald, Feb. 19 post). https://blogs.clemson.edu/regulatory/hornet-herald-9/
Yellow-Legged Ledger (2026). Yellow-Legged Hornet, Georgia Department of Agriculture. https://agr.georgia.gov/yellow-legged-hornet